Dhcp problem with ip phones

I have 5 FWS 648G PoE with two vlans on them : Data vlan is 101 and Voice vlan is 909. The firmware and the configs of the switchs haven't change since april. Since yesterday, if i unplug an ip phone and replug it, the phone will receive the dhcp from the dhcp server in the data vlan! All others phones are working well until I unplug them.

data vlan and voice vlan have each a separate dhcp server.

If I remote dual-mode from the port, the phone get the dhcp from the voice vlan, but as soom as I put back dual-mode, the ip phone receive the dhcp from the data vlan.

Here is a summary of the configuration of one switch, version is 07202a :

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